Siri is by far the iPhone 4S’s most-desired feature, and many non-4S users have been clamoring for hackers to make the voice assistant available on older iOS devices. While Siri ports have been demoed to the public before, it’s been made clear that public distribution is not possibile at this time due to legal issues.

Apple has made a Siri port legally possible with today’s iOS 5.0.1 revision by offering wide-open access to system files that were previously encrypted.

MuscleNerd, a prominent figure in the jailbreaking and hacking community, recently tweeted that the iOS 5.0.1 update from today features decrypted ramdisks, making it possible to extract the necessary files for a Siri port without infringing on Apple’s copyright. MuscleNerd said, “it’s the first public 4S ipsw where the main filesystem keys are obtainable (due to non-encrypted ramdisks).”

There have been multiple methods proposed for running Siri on non-4S hardware in recent weeks, but all of them are either illegal or impractical. To run Siri properly, one would need access to an iPhone 4S unique identifier and that key would need to be switched out every 24 hours to avoid detection. If thousands of devices start calling on Siri from one 4S identifier, Apple will be able to easily spot the activity and kill the port.

It’s unclear as to why Apple left such an opening for hackers to exploit when a Siri port has been such a hot topic as of late. iOS 5.1 is coming soon, and Apple may re-encrypt access to the 4S Siri files with its next update. Perhaps the second iOS 5.0.1 revision from today was rushed. Whether it be out of ignorance or some hidden agenda, Apple has made the possibility of a Siri port legal — at least for the time being.